Blade for a rotary machine

ABSTRACT

A blade for use in rotary machines such as a wind turbine blade has a plurality of dimples distributed over an area of a low pressure or suction surface of the blade which preferably extends from immediately adjacent to a leading edge of the blade at least partially towards a rear or trailing edge of the blade.

REFERENCE TO RELATED APPLICATION

This application claims priority to Irish Patent Application No.S2012/0347, filed Aug. 9, 2012, the disclosure of which is incorporatedherein by reference.

FIELD OF THE INVENTION

The present invention is concerned with a blade for a rotary machine,which in use undergoes driven or driving rotation, and is particularlybut not exclusively concerned with such blades when used in air or gasdriven applications such as a wind turbines, or air or gas driving ordisplacing applications such as fans, compressors, and blowers, and inparticular blades having improved flow characteristics, for examplereduced boundary layer separation, reduced turbulence, etc.

BACKGROUND OF THE INVENTION

Rotating blades are used in a large number of applications and inparticular rotary machines as described above, and in many of thoseapplications it is desirable to improve the efficiency and/orperformance of the blade through various means. In one applicationaerofoil blades are utilised in augmented wind turbine systems, forexample comprising a shroud surrounding a set of aerofoil blades such asto take advantage of the higher velocity profile. By improving theperformance and/or efficiency of such blades a greater power output canbe achieved and/or the turbines can be located in a more diverse rangeof locations. It will also be appreciated that the invention can be usedin conventional wind turbine systems or other rotational bladeapplications or machines.

As a further example, blades of various size, shape and design are usedin air displacers such as fans, compressors, blower based applications,for example HVAC applications, refrigeration applications, or any otherapplications requiring air or other fluid such as gas to be displaced.Such blades may have a full or partial aerofoil section, or may define asimple paddle/vane style blade design

It is therefore an object of the present invention to provide a blade orset of blades for a rotary machine having improved performance and/orefficiency.

SUMMARY OF THE INVENTION

According to the present invention there is provided a blade having aplurality of dimples distributed over an area of at least one surface ofthe blade which extends from at or adjacent a leading edge of the bladeat least partially towards a rear edge of the blade

Preferably, the blade comprises an aerofoil blade.

Preferably, the aerofoil comprises a low pressure or suction surface andan opposed high pressure or pressure surface, and the dimples aredistributed over at least an area of the low pressure surface.

Preferably, the aerofoil is asymmetric.

Preferably, the leading edge is rounded and the trailing edge is sharp.

Preferably, the area of dimples extends along at least a major part ofthe length of the blade.

Preferably, the dimples are generally teardrop-shaped with a wider endfacing towards the leading edge of the blade.

Preferably, the dimples vary in distribution density.

Preferably, the dimples vary in depth.

Preferably, the dimples vary in cross section with depth.

Preferably, the plurality of dimples comprises dimples of differentsize.

Preferably, the trailing edge of the blade has a localised rearward ordownstream extension.

Preferably, the localised rearward extension is at a free end of theblade.

Preferably, the blade is a wind turbine blade.

Preferably, dimples are also provided on the pressure surface of theblade.

As used herein, the term “dimple” is intended to mean a localiseddepression in a surface, and which may vary in cross section with depth,and may be of any suitable shape and orientation.

Various other objects, advantages and features of the present inventionwill become readily apparent to those of ordinary skill in the art, andthe novel features will be particularly pointed out in the appendedclaims.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be described, by way of example,with reference to the accompanying drawings, in which;

FIG. 1 is a perspective view of an embodiment of aerofoil bladeaccording to the invention, having particular application in a windturbine;

FIG. 2 is a schematic partial cross section through the blade of FIG. 1;

FIG. 3 is a partial top view of the blade of FIG. 1; and

FIG. 4 is a perspective view of a modification of the aerofoil blade ofFIG. 1.

DETAILED DESCRIPTION OF THE DRAWINGS

Referring to FIGS. 1 to 3, an aerofoil blade for use with a wind turbineis illustrated, and comprises an outwardly tapered blade 10 with arounded leading edge 12, and a sharp or narrow trailing edge 14 and anouter free end or tip 16. It will however be appreciated that the size,shape and profile of the blade 10 may be varied as required, dependingon the particular application with which the blade 10 is to be employed.A large number or array of dimples 18 are distributed over a lowerpressure or “suction” surface 20 of the blade 10, and as will bedescribed in detail hereinafter, are arranged to augment the flow of airaround the blade 10 in order to improve the performance and/orefficiency of the blade 10

In this particular embodiment the dimples 18 extend fully from theleading edge 12 of the blade to the trailing edge 14 and from the rootto the tip of the blade 10, i.e. they cover substantially the entiresuction surface 20. In general, however, the dimpled area of the upperor suction surface 12 may extend rearwardly from immediately adjacent tothe leading edge 12 of the blade 10 only partially to the trailing edge14, preferably at least one quarter the way to the trailing edge. Inaddition the dimples may not extend all the way to the root or the tip,and further alternatively the suction surface 12 may have one or moreregions devoid of dimples

Also, the dimpled area does not necessarily need to extend along thefull length of the leading edge 12 of the blade 10, although itpreferably extends along at least a major part of the length of theleading edge

In this embodiment the dimples 18 are generally concave teardrop-shapeddepressions aligned with their wider ends facing upstream towards theleading edge 12 of the blade, as shown in FIG. 3, and the narrow ortapered ends facing downstream towards the trailing edge 14. The dimples18 are preferably closely spaced, but their distribution density mayvary over the dimpled area. The dimples may also vary in depth, and mayvary in cross section with depth. It will also be appreciated that thedimples 18 may be of any other suitable shape or size in order togenerate a desired augmentation of the air flowing around the blade 10.In addition dimples 18 of different size, shape and/or depth may be usedon the same blade 10.

The dimples 18 can be created directly in the upper or suction surface20 of the blade, or by using blade protection tape 22 (FIG. 2) or anyother suitable carrier (not shown) which is embossed with the teardropor other shaped dimples 18 and applied to the upper surface 20. Thisallows the array of dimples 18 to be quickly and easily retrofitted toan existing blade.

In the embodiment shown in FIGS. 1 to 3 the length of the blade 10 was2.45 m with an average chord of 300 mm. The dimples are 15 mm long by 9mm wide at their widest part, with a maximum depth of 0.33 mm. Theseparticular dimensions are suited to wind turbine blades, and may ofcourse be varied to suit the intended application. For example in HVACor refrigeration applications, the blade 10 may be employed withrefrigeration fans, blowers and/or compressors (not shown) and willtherefore be dimensioned accordingly, with the profile of the blade 10being altered to suit the velocity profile of the gas being displaced.

The above turbine blade design serves to accelerate airflow, increaselift, reduce the wake created and/or increase the air displaced by theblade 10. The dimples 18 serve to create a micro-turbulent layer acrossthe blade 10 which in turn causes the wind-force acting on the blade tobe greater. The dimples delay boundary layer separation thereby reducingthe wake of the blade 10. The dimples 18, when in an inverted teardropshape, may also act as mini-augmenters and give the air direction. Thedepth, size, shape and distribution density of the dimples 18 may varywith blade characteristics or other system parameters.

In a modification of the above embodiment, FIG. 4, the trailing edge 14of the blade 10 has a localised rearward or downstream paddle-likeextension 24, preferably at its free end or tip 16. The extendedpaddle-like tip 24 of the blade 10 serves to increase the surface area.However the dimples 18 can still work effectively on a conventionalaerofoil blade which does not have the projection, i.e. as shown in FIG.1.

If desired, similar dimples may be provided on the “high pressure”surface of the blade (not shown), again extending rearwardly from theleading edge.

The present invention is not limited to the embodiment(s) describedherein, which may be amended or modified without departing from thescope of the present invention.

Therefore, it is intended that the appended claims be interpreted asincluding the embodiments described herein, the alternatives mentionedabove, and all equivalents thereto.

What is claimed is:
 1. A blade having a plurality of dimples distributedover an area of at least one surface of the blade which extends from ator adjacent a leading edge of the blade at least partially towards arear edge of the blade.
 2. A blade according to claim 1, comprising anaerofoil blade.
 3. A blade as claimed in claim 1, comprising a lowpressure or suction surface and an opposed high pressure or pressuresurface, and the dimples are distributed over at least an area of thelow pressure surface.
 4. A blade as claimed in claim 2, in which theaerofoil is asymmetric.
 5. A blade as claimed in claim 1, in which theleading edge is rounded and the trailing edge is sharp.
 6. A blade asclaimed in claim 1, wherein the area of dimples extends along at least amajor part of the length of the blade.
 7. A blade as claimed in claim 1,wherein the dimples are generally teardrop-shaped with a wider endfacing towards the leading edge of the blade.
 8. A blade as claimed inclaim 1, wherein the dimples vary in distribution density.
 9. A blade asclaimed in claim 1, wherein the dimples vary in depth.
 10. A blade asclaimed in claim 1, wherein the dimples vary in cross section withdepth.
 11. A blade as claimed in claim 1, wherein the plurality ofdimples comprises dimples of different size.
 12. A blade as claimed inclaim 1, wherein the trailing edge of the blade has a localised rearwardor downstream extension.
 13. A blade as claimed in claim 12, wherein thelocalised rearward extension is at a free end of the blade.
 14. A bladeas claimed in claim 1, wherein the blade is a rotary machine blade. 15.A blade as claimed in claim 1, wherein the blade is a wind turbineblade.
 16. A blade as claimed in claim 3, wherein dimples are alsoprovided on the pressure surface of the blade.
 17. A wind turbinecomprising at least one blade according to claim
 1. 18. An airdisplacement system comprising at least one blade according to claim 1.19. An air displacement system according to claim 18 comprising a fancomprising the at least one blade.